Why can't lpddr completely replace DDR?

LPDDR As low power Version of DDR, The bandwidth defined in the standard is even higher than that of the same generation DDR Higher , It seems that compared with DDR,LPDDR There are only advantages but no disadvantages , So why LPDDR Cannot completely replace DDR？ There are two possible reasons for thinking today , It's just for the purpose of attracting jade , If the boss you see has a better idea or wants to correct my opinion , Welcome to discuss .

Before introducing the specific reasons , Have a look first LPDDR comparison DDR The main difference between ： Low voltage （ It is also the main means to achieve low power consumption ）. Due to the same manufacturing process , The lower the supply voltage of the chip , The lower the working frequency the chip can achieve , In order to ensure the working speed ,LPDDR Made a trade-off , This corresponds to that it cannot be DDR Two possible reasons for substitution ：

1. In order to reduce the load circuit to ensure the clock frequency ,LPDDR Single channel Of DQ The data bit width is only 16bit, To achieve the same data bit width ,LPDDR You can only add more channel Put together （ For example, in order to achieve 32bit Data bit width , Two are needed channel Joint efforts ）, But this leads to a single package What can be provided in bank The small number , This reduces concurrency . however , Because each channel Less particles , And the length of the interconnection line is short ,LPDDR comparison DDR There is a higher nominal speed , for example ：LPDDR4 Maximum speed （ Single pin） by 4266MT/s, and DDR4 The maximum rate of is 3200MT/s.
Here are two die Put together a wider LPDDR device Example .

2. Due to low working voltage ,LPDDR Its internal working frequency is also low . To ensure bandwidth , You can only improve prefetching (prefetch) Number of digits ,DDR4 The prefetch of is 8bit, and LPDDR4 The prefetch of is 16bit,LPDDR5 The prefetch of is 16bit or 32bit. but LPDDR The increase of prefetch bits will also result in SOC When the access of is not continuous , The same read/write burst More data may be wasted in , This leads to a reduction in bandwidth utilization .